Cessna 150H N22507 accident near Vacaville, California

Probable cause

The partial loss of engine power due to a stuck exhaust valve.

NTSB analysis

The pilot was conducting a personal flight. During the initial climb after takeoff, the engine lost partial power, and the airplane was unable to maintain altitude. The pilot initiated a forced landing to a nearby field; during the landing roll, the airplane impacted uneven terrain and came to rest upright, which resulted in substantial damage to the left wing and fuselage.

Postaccident examination of the engine revealed that the No. 2 cylinder exhaust valve exhibited signatures consistent with a stuck valve, including a buildup of carbon deposits, and the exhaust valve could only be moved out of the valve guide with a significant amount of force. No additional evidence indicated any pre-existing mechanical malfunction or failure that would have precluded normal operation. Thus, the stuck exhaust valve likely caused the partial loss of engine power.

Text from the NTSB. Open the NTSB docket for WPR22LA316 for the full record.